(Fortune Magazine) -- The clock has just struck seven on a Thursday night, and Sheryl Sandberg is networking furiously. Not on Facebook, the site she joined in March as COO and where
she boasts 1,114 "friends." No, she's doing it the old-fashioned way, in her Atherton, Calif., living room. She hosts her Silicon Valley soirees a few times a year, and it's always
the A-list crowd. On this particular evening the group includes the new head of eBay North America, the manager of Google's ad-selling platforms, and well-known tech bankers and
venture capitalists. It's a high-wattage, high-powered group. Oh, and there's one other thing: All those attending are women.

As the wine flows, the room starts to buzz. In one corner Lorna Borenstein, president of online real estate service Move, plays Yahoo alumni geography ("Where are they now?") with
Caterina Fake, who co-founded Flickr and sold it to Yahoo (YHOO, Fortune 500). Author Sharon Meers, a former managing director at Goldman
Sachs, talks up her new book about dual-earner couples (there's a plug from Sandberg on the back cover). Near the piano, Stephanie Tilenius, who could be eBay's CEO someday, is
quizzing VCs about their latest deals. "We all rely on each other for advice and help each other out," Tilenius says.

These are the New Valley Girls. They are super-smart. Super-connected. And way too serious about their jobs and careers to endorse, much less embrace, that title. But the fact is,
these women are vastly different from their predecessors who broke Silicon Valley's glass ceiling in the 1980s and '90s. Former CEOs Carly Fiorina of Hewlett-Packard and Meg Whitman
of eBay hardly knew each other. "With us, it was heads down," says Whitman. She and Fiorina, who topped Fortune's Most Powerful Women list throughout the first eight years of its
11-year existence, didn't socialize with each other or much with other Valley stars. (Even now, as Whitman and Fiorina work to elect John McCain President, they know each other only
"kinda sorta," Whitman says.)

Unlike their predecessors, these next-generation women aren't interested in diligently climbing any corporate ladder. The 39-year-old Sandberg, who has taken on one of the toughest
assignments in tech, has already moved from the World Bank to McKinsey to the U.S. Treasury to Google to Facebook. Her friend Borenstein worked at Hewlett-Packard and Yahoo and eBay
before landing at Move (fitting, indeed!). A chance meeting with a private equity investor at Sandberg's house led her to that job last year. By socializing with one another,
Borenstein says, "we're putting ourselves in the pathway of opportunities."

While the old guard tended toward househusbands (the case for Fiorina and a third of the other women on Fortune's Most Powerful list historically), the new women leaders have power
marriages, young children, and lives tethered to tech. When Stephanie and Eric Tilenius married in 1999, they postponed their honeymoon and went on road shows instead - he for his
startup, Netcentives, and she for PlanetRx.com, which she co-founded. Now a mom with two children, 5 and 2, Tilenius, 41, squeezes in chats with other high-powered moms about kids and
careers during her morning drive to her eBay (EBAY, Fortune 500) office in San Jose.

As Google's (GOOG, Fortune 500) Sukhinder Singh Cassidy sees the situation, "We're hitting our
stride in our careers just as we're having children. We're not willing to give up the joys of either." Cassidy, 38, heads Google's vast Asia-Pacific and Latin American operations,
having expanded the unit from 17 employees to thousands based in 18 countries in five years. During the same time she married and had a daughter. She has logged close to 90,000 air
miles with Kenya, now 2. "If it's over a week, she comes with me. I just can't bear to be away from her," Cassidy says, noting that the logistics of her marriage to an investment
manager require "extensive negotiation."

Via Facebook and LinkedIn and Twitter, these women trade tips constantly. Kleiner Perkins partner Juliet Flint found her nanny with help from Borenstein. Anne Wojcicki, who runs DNA
startup 23andMe, has a baby due around Thanksgiving, so she's getting advice from her big sister, Susan, who is a mother of four - and a Google VP. "I don't do any work between six
and nine," says Susan. "No work. No e-mail. No nothing. I'm with my family. People at work adapt." She also outsources everything: shopping, cooking, housework. Meanwhile Sandberg and
her entrepreneur husband, Dave Goldberg, and their assistants and the nanny share a calendar - on Google, where else? Some couples work at rival companies, so they do the opposite.
Flint and her husband, Andre, live under a "code of silence," she says, because he invests with Sequoia and other VC firms with which Kleiner Perkins competes.

What has evolved here is a virtuous circle of women helping women navigate complex lives and career jungle gyms. "It's very self-reinforcing," says Susan Wojcicki, who famously rented
her garage to Larry Page and Sergey Brin, and there they started Google a decade ago. She compares it to something familiar to anyone, male or female, who has spent time in tech.
"It's the network effect."

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The theory of the network effect is this: The larger and more dynamic a network, the more valuable it becomes - a la eBay, which in its early form attracted buyers, which
attracted sellers, which attracted more buyers, and so on. Post-Meg Whitman, who built the first mega-community online, these women have taken lead roles in building social-networking
businesses. Jim Breyer of Accel Partners, who is on the Facebook board, says that the Valley's fastest-growing companies today "are about partnerships and teams." These Valley women
make good leaders in part because "they are deeply empathetic to helping each other succeed." If you think that their social web is completely self-sustaining, however, you're
mistaken. They rely heavily on powerful men.

Just ask Gina Bianchini. The onetime Goldman Sachs (GS, Fortune 500) analyst is CEO of Marc Andreessen's third startup, Ning. (The two
dated briefly years ago but are now married to other people.) The site lets consumers create their own social networks online. "I think it's a case of certain men taking certain risks
on certain women," says Bianchini, 36, "as opposed to, 'Women are social, so let's have them run social networks.'"

Similarly, Facebook's Sandberg says that her mentors have been men. The first key man in her life, besides her ophthalmologist father, was Larry Summers, who taught her economics her
junior year at Harvard. "She wasn't one of my students who raised her hand all the time, but when the midterm came, she got the best grade by some margin," recalls Summers, who went
on to be her thesis advisor. After working for Summers at the World Bank and later at Treasury, where he was Secretary, Sandberg was lured to Google by its new CEO, Eric Schmidt. She
headed Google's online sales and operations apparatus, building it from four people to 4,000, and also played a key role in shaping Google's culture. "We had a speaker series at
Google," Sandberg says, "and someone made the point that it was almost all men. So Susan Wojcicki and Marissa Mayer and I said we should have a women speaker series." They kicked it
off with Gloria Steinem and Jane Fonda. Nor did Sandberg think twice about working for a guy 15 years her junior. Last December, at former Yahoo COO Dan Rosenzweig's holiday party,
she met Mark Zuckerberg, then 23, who is the founder and CEO of Facebook. While most guests chatted with Zuckerberg "about random things," he recalls, he and Sandberg "talked about
scaling issues at a company, and it was actually smart. It was substantive." Sandberg soon hosted Zuckerberg to about a dozen dinners at her Atherton home - "about 50 hours," he says.
Two months after they first met, she left Google to be his No. 2.

Since they typically have wealthy spouses in tech or finance, these women can afford to do whatever they want - and with kids at home, they insist on it. "The attitude is, if I'm
going to stay in the workforce, I'm going to get a lot of satisfaction," says Trae Vassallo, a partner at Kleiner Perkins and a mother of two. The VC pool remains highly male (as
old-line partnerships tend to be). But Kleiner, which employed just two women VCs, Flint and Aileen Lee, seven years ago, now has seven women among its 29 partners.